Der mechanismus des korngrenzengleitens

Abstract

The glide of two grains of a polycrystal along their common grain boundary is caused by conservative motion of dislocations of a special structure within the grain boundary. These dislocations were found by electron microscopy of plastically deformed polycrystals. They are not related to the lattice dislocations of the adjacent grains. They exist only in grain boundaries and have therefore been named grain boundary dislocations (GBD). GBD can be made visible in the electron microsope and thus be examined thoroughly. The grain boundary is their glide plane and the Burgers vector lies within the grain boundary. The Burgers vector is not a lattice vector of the adjacent grains, but is the smallest possible glide vector necessary to restore the structure of the grain boundary after the passing of a GBD. The Burgers vectors depend solely on the structure of the grain boundary and they occur in all sizes and orientations. Undeformed polycrystals contain only a few or no GBD; they are formed during plastic deformation to produce grain boundary glide. Corners and Frank Read sources in the grain boundary are sources for GBD. GBD show interactions similar to those of lattice dislocations (pile-ups, networks). The grain boundary being the glide plane, the Burgers vector of the GBD has to change at bends in the grain boundary. This change leads to emission of lattice dislocations into the adjacent grains and therefore enables the grain boundaries to act as sources for lattice dislocations. The interaction of GBD with obstacles in the grain boundary (precipitates, alloy atoms, point defects, dislocations) is described. This interaction leads to grain boundary hardening (particle hardening and alloy hardening of grain boundaries). An atomistic model is given for the GBD by which all observed properties of the GBD can be explained.